Red Queen hypothesis

The hypothesis that organisms must continually evolve to maintain their relative fitness as competitors, predators, and parasites evolve.

Evolutionary arms race: Reciprocal adaptations in interacting species increase defensive and offensive capabilities over generations. Its escalating adaptations are a direct form of the reciprocal change described by the hypothesis.
Lewis Carroll: The English writer Charles Lutwidge Dodgson, author of Alice's Adventures in Wonderland. His Red Queen character gave the hypothesis its name through her account of running to stay in place.
Evolution of sex: The evolutionary emergence and persistence of sexual reproduction. The hypothesis helps explain how recombination can generate offspring parasites are less adapted to infect.
Court Jester hypothesis: The hypothesis that abiotic environmental change, rather than biotic interactions, chiefly drives macroevolutionary patterns. It contrasts with the Red Queen emphasis on interactions among evolving organisms.
Host–parasite coevolution: Reciprocal evolutionary change between parasites and their hosts. Parasites adapt to exploit hosts while hosts evolve resistance, creating continual selection on both.
Leigh Van Valen: The American evolutionary biologist who proposed the Red Queen hypothesis in 1973. He formulated the hypothesis to explain why extinction risk appeared constant across lineages.
Red Queen hypothesis of sex: An explanation for sexual reproduction in which genetic mixing helps hosts keep pace with parasites. This specific version applies Red Queen reasoning to the maintenance of sex.
Van Valen's law: The proposed pattern that extinction probability remains roughly constant over time within a taxonomic group. It is the empirical pattern Van Valen originally used to motivate his evolutionary explanation.
Frequency-dependent selection: Selection whose strength or direction depends on how common a trait is in a population. Rare host defenses or parasite strategies can gain an advantage, then lose it as they spread.
Extinction: The irreversible loss of a species when its last member dies. Van Valen's original argument concerned persistent extinction risk, not only host–parasite interactions.

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